Grinding mill

ABSTRACT

A grinding mill has a housing which includes a feed hopper and a downwardly converging chamber located below the feed hopper and having an upper region and a lower region which is provided with an outlet. A pair of cooperating grinding rollers are arranged in substantially axial parallelism in the upper region of the chamber spaced from the feed hopper and define with one another a grinding gap from which ground material drops into the lower region. A first pneumatic conduit conveys material to be ground from the region of the feed hopper to the region of the grinding gap. A feeding arrangement feeds the ground material from the lower region through the outlet into a second pneumatic conduit, and a suction conduit is provided which has one open end portion communicating with the second pneumatic conduit and another open end portion located proximal to the grinding gap. The suction conduit serves to aspirate air from the first pneumatic conduit into the second pneumatic conduit via the region of the grinding gap, so as to maintain suction in this region and also-via the first pneumatic conduit-in the feed hopper.

United States Patent Linzberger 1 Feb. 18, 1975 [541 GRINDING MILL229,939 12/1969 U.S.S.R 241/47 [75] Inventor: Robert Linzberger, SaintPrimary ExammerGranville Y. Custer, Jr. Gallen Bruggen SwltzeflandAssistant Examiner1-Ioward N. Goldberg 1 1 Assigneei Gebluedel'Bllehlel' UZWil, Attorney, Agent, or Firm-Michael S. Striker SwitzerlandFiled: Jan. 23, 1974 Applv No.: 435,854

Foreign Application Priority Data Jan. 24, 1973 Switzerland 1012/73 Dec.6, 1973 Switzerland... 17103/73 [52] US. Cl. 241/47, 241/225 [51] Int.Cl. B02c 23/02 [58'] Field of Search 241/47, 57, 58, 60, 62,

[56] References Cited UNITED STATES PATENTS 279,067 6/1883 Wolf 241/471,188,323 6/1916 Richardson. 241/57 1,991,757 2/1935 Lorentz 241/222 X2,925,226 2/1960 Pratique 241/225 3,167,259 1/1965 Pitchford 241/47 X3,468,488 9/1969 Karrer et al.. 241/225 X 3,545,686 12/1970 Brown 241/47FOREIGN PATENTS OR APPLICATIONS 2,011,783 12/1969 Germany 241/62 [57]ABSTRACT conduit conveys material to be ground fromthe region of thefeed hopper to the region of the grinding gap. A feeding arrangementfeeds the ground material from the lower region through the outlet intoa second pneumatic conduit, and a suction conduit is provided which hasone open end portion communicating with the second pneumatic conduit andanother open end portion located proximal to the grinding gap. Thesuction conduit serves to aspirate air from the first pneumatic conduitinto the second pneumatic conduit via the region of the grinding gap, soas to maintain suction in this region and alsovia the first pneumaticconduitin the feed hopper.

26 Claims, 7 Drawing Figures HTENTEU FEB 1 8 5 SHEET 2 BF 7 FIG. 2,

GRINDING MILL BACKGROUND OF THE INVENTION The present invention relatesto a grinding mill, and more particularly to a grinding mill whereinmaterial is ground between two cooperating grinding rollers definingwith one another a grinding gap.

Grinding mills of this general type are already well known and they arepart of the state of the art. They are used for grinding various typesof material that are admitted to the grinding gap via a feed hopper,frequently such materials as various types of foodstuffs. Generallyspeaking, the feeding of many of the materials to be ground proceedssatisfactorily in the prior-art grinding mills where the materialsupplied to the grinding gap has a substantially uniform veil ofmaterial. A pneumatic feed conduit is usedwhich serves to convey thematerial to the grinding gap, and at the air present at the end of thefeed conduit is aspirated along the periphery of at least one of thegrinding rollers in counterflow to the rotation of the same. Thiscounteracts the tendency of the rapidly rotating grinding roller to takealong the air in form of a boundary layer, and eliminates theinterference which would otherwise be caused with the proper flow of theveil of material into the grinding gap.

The continuous removal of ground material and its conveying away ispredominantly carried out in the prior art by a pneumatic suctionconveying conduit; in some instances. a pressure conveying conduit isutilized. A suction conveying conduit has the advantage that thenecessary suction which is required for the op eration of the pneumaticfeed conduit can be directly communicated from below the grinding gap toabove the grinding gap where the pneumatic feed conduit is located,whereas if a pressure conduit is used an injector will have to beinterposed.

However, despite the many advantages possessed by this prior art type ofgrinding mill, there are certain disadvantages which must be rectified.In particular, it is not readily possible to provide for a uniformfeeding via the pneumatic conduit of both lightweight and heavyweightmaterials to be ground, if uniform flowis to be achieved. To overcomethis difficulty, it would be necessary to vary the air flow in thepneumatic feeding conduit, since an air flow which may be correct forfeeding of heavyweight material may be excessive for lightweightmaterial where too much of the light-weight material might be carried bythe excessively strong air flow past the grinding gap and into theground-material part of the mill, especially when the grinding rollersoperate at high speed. However, the existing grinding mills cannot be soregulated to permit a variation in the air flow, and this thereforerepresents a substantial disadvantage.

SUMMARY OF THE INVENTION Accordingly, it is a general object of theinvention to provide an improved grinding mill which avoids theaforementioned drawbacks.

More particularly, it is an object of the present invention to providesuch an improved grinding mill wherein a reliable pneumatic feeding ofmaterial to be ground from the feed hopper to the grinding gap isassured under all circumstance, whether the material be light in weightor whether it be heavy.

Another object of the invention is to provide such an improved grindingmill which can be reliably and uniformly operatedeven at high rotationalspeed of its grinding rollers and at high throughput, i.e., incircumstances where a reliable and uniform feeding of the material to beground is highly questionable in the priorart constructions due to thestrong air currents which develop.

An additional object of the invention is to provide such an improvedgrinding mill in which any interference with the proper flow of thematerial and with the proper operation, resulting from variations inflow or pressure of air, will be reliably avoided.

Still a further object of the invention is to provide such an improvedgrinding mill wherein the various controls that most normally be carriedout during the operation of the grinding mill, for instance the takingof samples or the like, can be carried out without the undesired escapeof dust or the like, and in particular without causing any variation inthe grinding effect itself, so that all controls and all samples thatare taken will not be falsified by such undesiredinfluences.

In keeping with the above objects, and with others which will becomeapparent hereafter, one feature of the invention resides, in a grindingmill, in a combination which comprises wall means defining a' housingincluding a feed hopper and a downwardly converging chamber locatedbelow the feed hopper and having an upper region and a lower regionprovided with an outlet. A pair of cooperating grinding rollers arearranged in substantial axial parallelism in the upper region of thechamber spaced from the feed hopper and defining with one another agrinding gap from which ground material drops into the lower region.First pneumatic conduit means conveys material to be ground from theregion of the feed hopper to the region of the grinding gap. Secondpneumatic conduit means is provided, and feed means feeds groundmaterial from the lower region through the outlet into the secondpneumatic conduit means. Suction conduit means is provided, having oneopen end portion which communicates with the second pneumatic condiutmeans, and another open end portion which is located proximal to thegrinding gap for aspirating air from the first pneumatic conduit meansinto the second pneumatic conduit means via the region of the grindinggap, whereby to maintain suction in the region of the grinding gap andvia the first pneumatic conduit means in the feed hopper.

The novel features which are considered as characteristic for theinvention are set forth in the appended claims. The invention itself,however, both as to its construction and its method of operation,together with ad ditional objects and advantages thereof, will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is-a somewhat diagrammaticvertical section through a first embodiment of the invention;

FIG. 2 is a view similar to FIG. 1, illustrating a second embodiment ofthe invention;

FIG. 3 is a view similar to FIG. 2, illustrating a third embodiment ofthe invention;

FIG. 4 is a view similar to FIG. 3, illustrating a fourth embodiment ofthe invention;

FIG. is a view similar to FIG. 4, illustrating a fifth embodiment of theinvention;

FIG. 6 is a front view of another embodiment of the invention; and

FIG. 7 is a view similar to FIG. 1 but illustrating still a furtherembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring firstly to theembodiment illustrated in FIG. 1, it will be seen that reference numeral1 identifies a housing including two frames 2 (only one shown) which areconnected with one another by braces 3 extending normal to the plane ofthe drawing in FIG. 1, and by walls 4 extending in the same direction.Mounted in the housing are two grinding rollers 6 and 7 of which theroller 6 is usually driven at a higher speed of rotation than the roller7, with their direction of rotation being indicated by the arrows. Therollers 6 and 7 define with one another a grinding gap from which groundmaterial drops downwardly under the influence of gravity. The right-handside of the housing 1 in FIG. 1 is the front side, that is the sidewhich must be accessible to an operator, whereas the left-hand side isthe rear side.

The grinding mill is provided with a funnel-shaped hopper 9 whichextends over the entire length of the rollers 6, 7, Le, normal to theplane of FIG. 1, and which communicates with a feed arrangement using afeed roller 10 and a damming member 11, the latter of which is pivotablymounted for movement about a pivot axis 12. The feed roller 10 and thedamming member 11 together serve to distribute the material coming fromthe hopper 9, so that it will be supplied in form of an even veil ofmaterial into the grinding gap 15. The spacing of the member 11 withrespect to the flows between them towards the gap 15, can beautomatically regulated in a manner which is known per se and,therefore, need not be described herein. The inlet baffle 13 of apneumatic feed channel is arranged downstream of the feed roller 10 andserves to guide the material from the feed roller 10 into the pneumaticfeed channel 14 wherein it is conveyed to the grinding gap 15.

The walls 4 of the housing form a closed interior for the housing,except for the presence of aspiration openings 22 which will bediscussed later, in which suction can be maintained to prevent theescape of dust and the like. The lower portion of the housing isconfigurated as a funnel-shaped region 19 which communicates via a loweroutlet (shown, but not separately provided with a reference numeral)with a feeding arrangement through which ground material is removed fromthe funnel-shaped chamber 19.

In the region of the rollers 6, 7 the walls 4 are so con-v feed roller10, and thereby the quantity of material that tion conduit through whichthe ground material is removed. The conduit 31 is connected with anappropriate source of suction (not shown) and the injector 30 isprovided with an inlet nipple 43 through which additional air may beallowed to enter, if necessary.

At the front side the grinding mill is provided in the upper region witha control flap 21 which forms an aspiration opening 22 together with theguide baffle 17, which opening 22 extends over the entire length (indirection normal to the plane in FIG. 1) of the housing. In the regionof the gap 15, the channels 18 are provided with a throttle gap 23, andthe channel 18 associated with the grinding roller 6 is formed in theregion of the gap 15 with an aspiration-controlling slide 24. A suctionconduit 41 extends to the region of the periphery of the roller 7,having an inlet end proximal to the grinding gap 15 and an outlet endwhich is connected with the conduit 31. A throttle 42 which in theillustrated embodiment is adjustable. is interposed in the suctionconduit 41.

It will be appreciated that in operation, the material to be ground isadmitted into the hopper 9 from where it is conveyed by the rotatingfeed roller 10 into the feed channel 14. A quantity of material beingconveyed can be controlled by pivoting the member 11 so that it definesa larger or smaller gap with the periphery of the feed roller 10. Theair that is being drawn through the feed channel 14 due to the suctionexerted by the suction conduit 41, accelerates the material in the feedchannel 14 and causes it to enter into the grinding gap 15 where it isground.

It is an essential concept of the invention that the air flow conditionsare controlled and maintained in optimum parameters in each operatingcondition of the mill. This is done by the presence of the suctionconduit 41 which, because of the manner in which it communicates withthe gap 15 and the channel 14, makes it possible to provide such acontrol in the region of the gap 15. In particular, the presence of thechannel 41 makes it possible to maintain suction in the region of thegap 15 and thus also in the channel 14 and, to someextent, also in thehopper 9. Air is also drawn into the condiut 41 via the openings 22.

The channel 14- constitutes with the conduit 41 an independent feedingand air system, which makes'possible an optimum feeding of material tothe gap 15, irrespective of the particular'type of material which is tobe ground, and even at high speed rotation of the roller 6, 7 and highthroughput of material. The air flow in the channel 14 can be regulated,if necessary, by operating the throttle 42. The material supplied by thefeed roller 10 is engaged by the air stream entering the channel 14 inthe region of the inlet baffle 13, and is accelerated and flung atrelatively high speed into the grinding gap 15. The air which issues inthe region of the grinding gap 15 from the channel 14 is predominantlydrawn into the suction conduit 41 and from there enters the conduit 31where it serves as the conveying medium for the ground material whichtravels in the conduit 31. A part of the air which enters through theopening 22 is diverted via the slide 24 into the channel 18 and servesto introduce the ground material into the injector 30.

Theeffectiveness of the novel construction,'and the fact that theobjects ofthe invention are achieved by it, can be readily demonstratedby removing a sample of the ground material. For this purpose, the door26 is opened and it has been found that the air which is now drawn inthrough the opeining exposed by the door 26 does in no way influence thepneumatic feeding of material in the channel 14 or the conduit 31. Thereason for this is that the air which is required for such feeding nowenters at least in part through the opening exposed by the door 26,instead of enteringas previously via the slide 24. It has also beenfound that the uniform supply of material to the grinding gap 15 is inno way influenced by opening the door 26, because the air flow conditionin the channel 14 is not varied thereby. This means, of course, that thegrinding operation is not at all influenced when the door 26 is opened,a condition which is highly advantageous because it is, of course,necessary if a proper sample is to be obtained.

The throttle 42 could be omitted, if desired, but in many instances itspresence will be effica cious because it permits a control of the airflow, the pressure conditions and largely also the material flowconditions in the grinding gap 15,- if and when necessary. The air flowcould, of course, also be obtained in accordance with a desiredparameter by appropriate dimensioning of the conduit 41 and/or theconduit 31.

As will be seen subsequently in the discussion of FIG. 3, the injector30 could be eliminated in favor of a bucket wheel 44, but even in thiscase it is advantageous to aspirate the chamber 19. If additional air isrequired to be admitted for the operation, particularly in the lowerportion of the conduit 3] intermediated the injector 30 and the pointwhere the conduit 41 communicates with the conduit 31, then suchadditional air can be admitted via the inlet nipple 43 of FIG. 1.

Coming now to the embodiment in FIG. 2, it will be seen that this isreminiscent of that in FIG. 1, and that like reference numerals havebeen used to define like elements. In this embodiment, however, thesuction conduit is identified with reference numeral 27 and extendspartly around the periphery of the roller 7 and along the rear wall ofthe housing or more particularly of the funnel-shaped chamber 19. Inorder to prevent any interference in the proper operation of the suctionconduit 27, for instance due to varying pressure conditions in thechamber 19, a seal 28 is interposed between the roller 7 and the conduit27, so that the latter cannot directly communicate with the chamber 19.

It is advantageous to provide the injector 30 with a regulating baffleor adjustable control flap 30 to more effectively control the air flowconditions in the channel 14 and the feeding conditions in the ejector30. This is a particularly advantageous arrangement because theadvantages of the invention can be obtained with a very simpleconstruction, and in particular no separate conduit is required whichcould interfere with the manipulations of personnel required to work onthe mill.

Coming to the embodiment of FIG. 3, which again uses like referencenumerals for like elements as in the preceeding embodiments, it will beseen that here the member 11 of FIG. 1 is replaced by a baffle 61 whichis already known per se from the art and which is mounted for turningmovement about a pivot 62. The purpose and operation of the member62 isthe same as that of the member 11. The baffle 62 is provided with alongitudinally extending (normal to the plane of FIG. 3) arcuatelycurved portion 63 in order to guide the material to the inlet baffle 13of the feed channel 14.

In this embodiment, a compartment 65 is provided which is in partdefined by the periphery of the grinding roller 6; it serves primarilyto accommodate the air which issues-from the outlet end of the channel14 and which is withdrawn via the suction conduit 66 that communicateswith the compartment 65. The air flow could be regulated by an openingthe cross section of which could be controlled if desired.

The suction conduit 66 communicates with the con duit 31 via a conduitportion that connects it first with the bucket wheel 44 interposed inthe outlet of the chamber 19 and then with the lower end of the conduit31. The bucket wheel 44 turns and discharges the ground materialaccomodated in each of its buckets or divisions, into the conduit whichcommunicates with the conduit 31. A small gap 68 exists between thechannel l4 and the roller 7, and a small amount ofthe air issuing fromthe channel 14 escapes from this-gap 68 along the roller 7 and into thechamber 19. The chamber 19 can be placed under suction, for instance viathe conduit 66. This embodiment, incidentally, has the advantage thatdue to the cross-sectional configuration of the chamber 19 it ispossible to locate the drive motor 69 which drives the rollers 6, 7 and10 in a manner not illustrated, but conventional, within the housinginter mediate the two frames 2 thereof, thereby both affording goodaccess to the drive and at the same time providing a space-savingconstruction.

The embodiment in FIG/4 is reminiscent of that in FIG. 3, and likereference numerals identify like components as before. In FIG. 4,however, the suction conduit 66 is connected with the suction side of ablower 71. The pressure side of the blower 71 communicates with aconduit 72 which in turn is connected with the concuit 31, and injector67 being formed which corresponds to the injector 30 of FIG. 1 instructure and in operation. In this particular embodiment, the conduit31 could be operated as a pressure conduit or as a suction conduit,depending upon particularrequirements, by making simple modifications toconvert from one type to another.

The embodiment of FIG. 5 is also reminiscent of that in FIGS. 3 and 4.Here, the conduit 72 is 'connectedvia an outlet 81 with the lowerportion of the chamber 19.

A curved injector 82 communicates the outlet of the chamber 19 with theconduit 31.

In this embodiment, the orientation ofthe outlet 81 is such that airwhich is expelled from it into the chamber 19 has a main component offlow which is directed towards the injector 82. This embodiment isparticularly suitable if materialis to be ground, and subsequentlyinserted into the conduit 31, which is difficult to convey and where theparticular effect of the air stream issuing from the outlet 81 isrequired in order to aid the entry of the material into the injector 82.A seal is provided between the wall 84 of the channel 14 and the roller7, to prevent the entry of air which travels around with the peripheryof the roller 7, into the grinding gap 15.

In FIGS. 35 I have illustrated how the suction conduit 66 can be locatedin part at least outside the housing of the grinding mill. FIG. 6, bycontrast, shows that a much more space-saving construction can be obtained if the suction conduit 66 is so located that it is laterallyadjacent the chamber 65, which can be given the configuration of thechamber 19 in FIG. 6, for example, and if the conduit 66 extneds alongthe frames 2 to the injector 67 and from there communicates with.

the conduit 31. In all other respects, the embodiment of FIG. 6corresponds to the preceding embodiments.

FIG. 7, finally, illustrates yet a further embodiment of the inventionwhich is highly advantageous. Like reference numerals again identify thesame elements as in the preceding embodiments.

In FIG. 7, however, the feed hopper 9 has located in it a rotating vanewheel 16 or the like, which serves to constantly loosen up the materialin the hopper 9 and prevent it from caking. The suction conduit 27extends partly about the periphery of the roller 7 and extends along therear wall 4 bounding the chamber 19, in a manner analogous to FIG. 2. Aseal 28 is provided between the conduit 27 and the roller 7 to preventinterference of pressure variations in the chamber 19 with theconditions in the conduit 27.

in order to assure that the air conditions in the channel 14 and thefeeding conditions in the injector 30 can be regulated at will, a flap30 is provided in association with the injector 30. This is aparticularly advantageous solution, because the control can be effectedwith very simple means. The flap 30' is, of course, pivotable about theindicated pivot axis, as is the flap 30' in FIG. 2.

The rear end wall portion 97 bounding the chamber 19 is removable, so asto facilitate access to the interior, particularly to the lower part ofthe conduit 27 and to the injector 30. An upright hollow shaft 90 ispro-' vided which constitutes an extension of the conduit 27 and reachesto the upper edge 91 of the housing 1, or to the level of the hopper 9.The upper open end of the shaft 90 is closed from the outside by aclosure member 92 which is advantageously of wood, as illustrated in thecross-sectional showing of FIG. 7, and which airtightly closes the openend of the shaft 90 with a flange 93. A portion 94 of the member 92extends into the shaft 90 and has a side facing towards the interior ofthe hopper 9 and being arcuately curved so that an opening 95 whichcommunicates the hopper 9 with the shaft 90 is provided with anaerodynamically advantageous cross section.

A flap 96 is provided which can increase or decrease the effective crosssection of the opening 95. The flap 96 could be replaced with anothercontrol member, for instance a sliding member or the like, andappropriate levers can be utilized for effecting this movement from theexterior of the mill. The flap 96-or analogous element must be soconfigurated that material which drops into the hopper 9 in thedirection of the arrow, cannot enter into the opening 95 and thus cannotbe carried along by the air stream which enters from the hopper 9through the opening'95 into the shaft 90. On the other hand, there isnothing to interfere with the entry of such air through the opening 95,which means that excess air is removed from the hopper 9 and the escapeof dust and the like is suppressed. Thus, the hopper 9 is constantlyunder a slight suction.

The rather surprising advantage which has been observed in connectionwith this embodiment is that both the conditions of air prevailing inthe gap and the conditions of the air in the hopper 9 are both activelycontrollable with this embodiment. The quantity of air for the channel14 and the excess air in the hopper 9 can both be removed and can befully utilized for the pneumatic transportation of ground material whichadvances in the conduit 31. 9

Together with the construction of the hopper 9, the flap 96 or itsanalogous replacement consititutes a separator, inasmuch as very fineparticles constituting a part of the material admitted into the hopper 9can be carried by the air through the opening 95 and into the shaft 90.This is permissible because such very fine parts which are smaller thanthe particles of ground material can, of course, readily be admixed withthe ground material particles without any difficulties. This solutionmakes it possible to eliminate many additional conduits, blowers,filters and the like, which were previously necessary, because theconduit 31 makes it possible to appropriately and properly control theentire air flow and air pressure conditions in the mill, and to regulatethem to an optimum extent. 7

Particularly if the grinding mill according to the present invention isused for grinding foodstuffs for human use, for instance various grainsor the like, it is frequently necessary to remove samples of the groundmaterial directly from the chamber 19, in order to test for possiblechanges in the dimension of the gap 15 and consequent changes in thegranulation of the ground product, changes in the moisture content orthe like. For this reason, all grinding mills of the type in questionare provided with a control door 26 through which such access isafforded. As previously already indicated, the advantages of the presentinvention are particularly emphasized when one attempts to remove such asample, because the opening of the control door 26 in a grinding millaccording to the present invention in no way influences the air flow andair pressure conditions in the grinding mill, and thus can under nocircumstances disadvantageously. influence the operation of the mill.

The shaft 90 in the embodiment of FIG. 7 could, if desired, be providedwith the member 92v at a lower level, and laterally rather than on top.However, in most instances it has been found that the location shown inFIG. 7 is the most advantageous one. It will be appreciated from aconsideration of FIG. 7 that both the shaft 90 and the conduit 27 can besimply and readily cleaned if and when this is necessary, aconsideration which is important in particularly those instances wherefoodstuffs for human consumption are being ground.

In addition to overcoming the disadvantages of the prior art, and thusmeeting the objects of the invention, the grinding mill according to thepresent invention improves on the economy of operation which heretoforecould be obtained with analogous grinding mills. Moreover, thetransportation of ground material from the chamber 19 is completelyindependent of the supply of material to the grinding gap, and thegrinding of the material in the gap. This means that in particular theentry of the material from the hopper 9 to the grinding gap 15 can becontrolled to conditions which are considered optimum, under allcircumstances and without having to consider the removal of the groundmaterial. The infiltrated air" which enters when the door 26 is openedfor removal of a sample or the like, does in no way influence the properoperation, such as the grinding itself, and thus it is now possible toobtain a sample which is not falsified by a temporary change in theoperating conditions that occurs in the prior art when a door similar tothe door 26 is opened.

. The air required for the transportation of material in the channel 14can in its entirety be used for subsequent transportation of groundmaterial in the-conduit 31, without requiring separate aspirationdevices.

It goes without saying that the channels 18 may be provided for only oneof the rollers 6 or for both of them. It is particularly advantageous ifthey are provided for both of the rollers, because this eliminates theso called fioating" of material and causes a partial cooling of therollers which is desirable. In the case of embodiments such as those inFIGS. 4 and wherein a blower 71 is utilized, the conduit 31 can beoperated as a pressure conduit, rather than as a suction conduit.However, if desired, it can nevertheless be in addition connected with asource of suction, in whichcase the conveying effectiveness will befurther enhanced. However, it is then important to assure that theconnection of the pressure side of the blower, such as the blower 71,with the conduit or passage having the feeding arrangement (such as thebucket wheel or the injector) therein be at the upstream side of thefeeding arrangement.

The arrangement of FIG. 6 is particularly advantageous in terms of itsreduced space requirements, because due to the fact that the conduit orconduits 66 are located laterally of the chamber 65 (equivalent to thechamber 19) extending along the back thereof, reduces the depth of themill from the front towards the rear side thereof. It is particularlyadvantageous in applications where space is at a premium and where twoof the grinding mills must always be arranged back-toback.

In the embodiment of FIG. 7, it is conceivable to eliminate the movableflap 96 (or its equivalent movable element) in favor of an opening 95havine a fixed preselected effective cross-sectional area. The area canbe readily determined empirically, independence upon the requirementswhich are made in a particular instance.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the type described above.

While the invention has been illustrated and described as embodied in agrinding mill, it is not intended to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. In a grinding mill, a combination comprising wall means defining ahousing including a feed hopper and a downwardly convergent chamberlocated below said feed hopper and having an upper region and a lowerre-- gion provided with an outlet; a pair of cooperating grindingrollers arranged in substantial axial parallelism in said upper regionof said chamber spaced from said feed hopper and defining with oneanother a grinding gap from which ground. material drops into said lowerregion; first pneumatic conduit means for conveying material to beground from theregion of said feed hopper to the region of said grindinggap; second pneumatic conduit means; feed means for feeding groundmaterial from said lower region through said outlet into said secondpneumatic conduit means; and suction conduit means having one open endportion communicating with said second pneumatic conduit means, andanother open end portion located proximal to said grinding gap foraspirating air from said first pneumatic conduit means into said secondpneumatic conduit means via the region of said grinding gap, whereby tomaintain suction in the region of said grinding gap.

2. A combination as defined in claim'l, wherein said other open endportion is located adjacent the periphery of one of said grindingrollers.

3. A combination as defined in claim 1; and further comprising sealingmeans interposed between said one grinding roller and part of an edgebounding said other open end portion.

4. A combination as defined in claim 2, wherein said feed meanscomprises injector means for feeding the ground material by injectoraction into said second pneumatic conduit means,

5, A combination as defined in claim 4, wherein said injector meanscomprises an adjustable control flap for varying said injector action.

6. A combination as defined in claim 1, wherein said chamber isfunnel-shaped and has a front wall and a rear wall; and wherein saidsuction conduit means extends along said rear wall.

7. A combination as defined in claim 6, wherein said suction conduitmeans forms a passage which extends partly about the periphery of one ofsaid grinding rollers and is in part defined by said periphery.

8. A combination as defined in claim 6, wherein said suction conduitmeans includes a substantially vertical hollow shaft extending in theregion of said rear wall from said lower region to the region of saidfeed hopper.

9. A combination as defined in claim 8, wherein said shaft has anopening; and further comprising remov able closure means which movablycloses said opening of said shaft..

10. A combination as defined in claim 9, wherein said opening of saidshaft is located in the region of said feed hopper. Y

11. A combination as defined in claim 8, wherein said shaft has anopening which communicates with the interior of said feed hopper; andfurther comprising varying means for varying the effective cross sectionof said opening of said shaft so that, depending upon the suctionexerted in said feed hopper via said opening of said shaft, lightweightcomponents of the material admitted into said feed hopper can bewithdrawn from the latter and into said shaft via said opening of saidshaft.

12. A combination as defined in claim 11, wherein said varying meanscomprises a pivotally suspended flap which is so configurated as todirect material which is being admitted into said hopper away fromopening said shaft.

13. A combination as defined in claim 11, wherein said varying meanscomprises a slide member which is so configurated as to direct materialwhich is being admitted into said hopper, away from said opening of saidshaft.

14. A combination as defined in claim 11, wherein said shaft has anadditional opening located upwardly of the first-mentioned opening; andfurther comprising a removable closure member closing said additionalopening and having a portion which extends into said shaft towards saidfirst-mentioned opening, said portion of said closure member having aside facing towards said first-mentioned opening and being rounded so asto define a flow guide for matter entering via said first-mentionedopening.

15. A combination as defined in claim 1, wherein said first pneumaticconduit means forms a throttling gap with one of said grinding rollers.

16. A combination as defined in claim 1; and further comprisingthrottling means interposed in said suction conduit means.

17. A combination as defined in claim 16, wherein said throttling meanscomprises an adjustable throttling flap for varying the suction whichacts in the region of said grinding gap and in said feed hopper.

18. A combination as defined in claim 1, wherein said wall meanscomprises a wall portion which together with one of said grindingrollers defines a compartment that communicates with said grinding gap;and wherein said other open end portion of said suction conduit meanscommunicates with said compartment.

19. A combination as defined in claim 1; and further comprising meansdefining a throttling gap between one of said grinding rollers and saidother open end portion of said suction conduit means.

20. A combination as defined in claim 1; and further comprising blowermeans having a suction side connected with said suction conduit means,and a pressure side connected with said first pneumatic conduit meansupstream of said grinding gap.

21. A combination as defined in claim 20, wherein said feed meanscomprises a conduit communicating with said outlet and with said suctionconduit means; and wherein said suction side of said blower meanscommunicates with said conduit upstream of said outlet and said suctionconduit means.

22. A combination as defined in claim 20, wherein said feed meanscomprises injector means communicating with said outlet; and whereinsaid pressure side of said blower means has a discharge opening whichcommunicates with the interior of said chamber in said lower region andhas such an orientation that air expelled from said opening has a majorcomponent of movement in direction towards said outlet.

23. A combination as defined in claim 1, wherein said feed meanscomprises a bucket wheel.

24. A combination as defined in claim 1, wherein said feed meanscomprises injector means.

25. A combination as defined in claim 1; and further comprisingaspiration openings provided in said wall means and communicating withthe interior of said housing.

26. A combination as defined in claim 1; and further comprising curvedguide baffle means defining with at least one of said grinding rollersan air channel which partly surrounds the periphery of said one grindingroller and communicates with said chamber.

1. In a grinding mill, a combination comprising wall means defining ahousing including a feed hopper and a downwardly convergent chamberlocated below said feed hopper and having an upper region and a lowerregion provided with an outlet; a pair of cooperating grinding rollersarranged in substantial axial parallelism in said upper region of saidchamber spaced from said feed hopper and defining with one another agrinding gap from which ground material drops into said lower region;first pneumatic conduit means for conveying material to be ground fromthe region of said feed hopper to the region of said grinding gap;second pneumatic conduit means; feed means for feeding ground materialfrom said lower region through said outlet into said second pneumaticconduit means; and suction conduit means having one open end portioncommunicating with said second pneumatic conduit means, and another openend portion located proximal to said grinding gap for aspirating airfrom said first pneumatic conduit means into said second pneumaticconduit means via the region of said grinding gap, whereby to maintainsuction in the region of said grinding gap.
 2. A combination as definedin claim 1, wherein said other open end portion is located adjacent theperiphery of one of said grinding rollers.
 3. A combination as definedin claim 1; and further comprising sealing means interposed between saidone grinding roller and part of an edge bounding said other open endportion.
 4. A combination as defined in claim 2, wherein said feed meanscomprises injector means for feeding the ground material by injectoraction into said second pneumatic conduit means.
 5. A combination asdefined in claim 4, wherein said injector means comprises an adjustablecontrol flap for varying said injector action.
 6. A combination asdefined in claim 1, wherein said chamber is funnel-shaped and has afront wall and a rear wall; and wherein said suction conduit meansextends along said rear wall.
 7. A combination as defined in claim 6,wherein said suction conduit means forms a passage which extends partlyabout the periphery of one of said grinding rollers and is in partdefined by said periphery.
 8. A combination as defined in claim 6,wherein said suction conduit means includes a substantially verticalhollow shaft extending in the region of said rear wall from said lowerregion to the region of said feed hopper.
 9. A combination as defined inclaim 8, wherein said shaft has an opening; and further comprisingremovable closure means which movably closes said opening of said shaft.10. A combination as defined in claim 9, wherein said opening of saidshaft is located in the region of said feed hopper.
 11. A combination asdefined in claim 8, wherein said shaft has an opening which communicateswith the interior of said feed hopper; and further comprising varyingmeans for varying the effective cross section of said opening of saidshaft so that, depending upon the suction exerted in said feed hoppervia said opening of said shaft, lightweight components of the materialadmitted into said feed hopper can be withdrawn from the latter and intosaid shaft via said opening of said shaft.
 12. A combination as definedin claim 11, wherein said varying means comprises a pivotally suspendedflap which is so configurated as to direct material which is beingadmitted into said hopper away from opening said shaft.
 13. Acombination as defined in claim 11, wherein said varying means comprisesa slide member which is so configurated as to direct material which isbeing admitted into said hopper, away from said opening of sAid shaft.14. A combination as defined in claim 11, wherein said shaft has anadditional opening located upwardly of the first-mentioned opening; andfurther comprising a removable closure member closing said additionalopening and having a portion which extends into said shaft towards saidfirst-mentioned opening, said portion of said closure member having aside facing towards said first-mentioned opening and being rounded so asto define a flow guide for matter entering via said first-mentionedopening.
 15. A combination as defined in claim 1, wherein said firstpneumatic conduit means forms a throttling gap with one of said grindingrollers.
 16. A combination as defined in claim 1; and further comprisingthrottling means interposed in said suction conduit means.
 17. Acombination as defined in claim 16, wherein said throttling meanscomprises an adjustable throttling flap for varying the suction whichacts in the region of said grinding gap and in said feed hopper.
 18. Acombination as defined in claim 1, wherein said wall means comprises awall portion which together with one of said grinding rollers defines acompartment that communicates with said grinding gap; and wherein saidother open end portion of said suction conduit means communicates withsaid compartment.
 19. A combination as defined in claim 1; and furthercomprising means defining a throttling gap between one of said grindingrollers and said other open end portion of said suction conduit means.20. A combination as defined in claim 1; and further comprising blowermeans having a suction side connected with said suction conduit means,and a pressure side connected with said first pneumatic conduit meansupstream of said grinding gap.
 21. A combination as defined in claim 20,wherein said feed means comprises a conduit communicating with saidoutlet and with said suction conduit means; and wherein said suctionside of said blower means communicates with said conduit upstream ofsaid outlet and said suction conduit means.
 22. A combination as definedin claim 20, wherein said feed means comprises injector meanscommunicating with said outlet; and wherein said pressure side of saidblower means has a discharge opening which communicates with theinterior of said chamber in said lower region and has such anorientation that air expelled from said opening has a major component ofmovement in direction towards said outlet.
 23. A combination as definedin claim 1, wherein said feed means comprises a bucket wheel.
 24. Acombination as defined in claim 1, wherein said feed means comprisesinjector means.
 25. A combination as defined in claim 1; and furthercomprising aspiration openings provided in said wall means andcommunicating with the interior of said housing.
 26. A combination asdefined in claim 1; and further comprising curved guide baffle meansdefining with at least one of said grinding rollers an air channel whichpartly surrounds the periphery of said one grinding roller andcommunicates with said chamber.